Exercise Reverses Some Effects of Fatty Meals
Vitamin C and Blood Pressure
EXERCISE REVERSES SOME EFFECTS OF FATTY MEALS
The cells lining the interior of our bodies’ blood vessels do more than just provide a smooth surface over which blood cells can glide without forming dangerous blood clots. These vascular endothelial cells also regulate the tone and diameter of our blood vessels, including the critical vessels that supply blood to the heart, brain, kidneys, and other vital organs. Complex biochemical feedback loops control the synthesis of nitric oxide, and other chemicals, from within the vascular endothelial cells, enabling blood vessels to dilate up when the organs that they serve require additional blood flow. When this “demand-related” dilation of blood vessels is impaired, vital organs, including the heart, can become starved of life-sustaining oxygen due to reduced blood flow (also known as ischemia). In addition to potential ischemia, other adverse physiological effects are also associated with inadequate blood vessel dilation, or vasodilation. These adverse factors include an increase in vascular resistance that can strain the heart, an increased risk of potentially dangerous clots within blood vessels, and increased inflammatory activity that can accelerate atherosclerosis (narrowing of the arteries) and organ damage.
There are multiple known risk factors for decreased vascular endothelial cell function, including elevated cholesterol levels, high blood pressure, obesity, diabetes, smoking, atherosclerosis, and increasing age. Interestingly, merely eating a fatty meal can rapidly induce vascular endothelial cell dysfunction, leading to a decrease in nitric oxide synthesis by these cells. When this happens, arteries become stiff, and can no longer dilate up to provide increased blood flow when required. When coronary arteries are already narrowed and diseased by atherosclerosis, a sudden loss of nitric oxide from endothelial cells can result in a critical lack of blood supply to the heart’s muscle, causing myocardial ischemia, as well as the formation of blood clots within severely narrowed coronary arteries. This, in turn, can result in a complete obstruction of the coronary arteries, causing a heart attack (myocardial infarction). Similar events can occur in the brain, causing a stroke.
It is known that vigorous exercise can improve vascular endothelial cell function, although the precise mechanisms at work are not entirely understood at this time. However, just as regular and vigorous exercise helps to keep our bodies looking and feeling young, overall, so does exercise also appear to keep our blood vessels young, supple, and able to dilate up to provide increased blood flow when required. Now, a newly published study in the Journal of the American College of Cardiology looks at the ability of exercise to prevent vascular endothelial dysfunction following a fatty meal.
In this study, 8 healthy adult males were fed high-fat meals. All patient volunteers underwent vascular testing before and after consuming the high fat meals in order to assess the level of endothelial cell dysfunction in the artery that supplies the arm. The experiment was varied such that each high-fat meal was preceded by either a 16 to 18 hour period of rest, a similar period of moderate-intensity exercise, or by a similar period of high-intensity exercise. The ability of the brachial artery to dilate up under conditions requiring increased blood flow was then measured under each of these three experimental conditions.
Following consumption of a high-fat meal, the brachial arteries of the men who had rested before eating narrowed, on average, by about 10 percent from their pre-meal baseline diameter, confirming the onset of significant endothelial cell and arterial dysfunction. The men who engaged in moderate-intensity exercise prior to their super-sized meals also experienced a 10 percent reduction in the diameter of their brachial arteries after consuming their high-fat meals, just like the men who rested before they ate. However, even these moderate levels of exercise did restore some (but not all) of their arteries’ ability to dilate in response to increased blood flow requirements, whereas there was no return of this flow-mediated vasodilation in the arteries of the men who had rested prior to eating. Among the men who engaged in vigorous, high-intensity exercise prior to chowing down, however, arterial dilation in response to increased blood flow was preserved even after a high-fat meal. This protective effect of high-intensity exercise on vascular endothelial function following a high-fat meal occurred despite laboratory evidence of increased fat and cholesterol levels in the blood of these same men after eating.
While I am certainly not suggesting that it is safe to gorge on high-fat foods as long as you exercise like a maniac before you eat, this clinical study nonetheless suggests that at least one adverse cardiovascular effect acutely associated with eating a fatty meal can be substantially prevented with exercise, but only when that exercise is performed before eating, and at a very high intensity level. On the other hand, this research study cannot provide any reasonable assurance that all of the other adverse and life-threatening health effects of high-fat diets (including cancer) can be prevented by exercising before meals, even if you exercise like crazy!
VITAMIN C AND BLOOD PRESSURE
The past few years have not been very kind to antioxidant vitamins like Vitamin C, Vitamin E, and Vitamin A and its derivatives. Large-scale, high-powered prospective clinical trials have recently dashed prior hopes that these vitamins can significantly reduce the risk of cancer or cardiovascular disease. Despite intriguing results from earlier and much lower powered research studies, we simply have not been able to show that any of these potential health benefits are associated with antioxidant vitamin supplements in humans. However, a new clinical research study in the Nutrition Journal suggests that there may still be some potential long-term cardiovascular health benefit from high Vitamin C levels in the blood.
High blood pressure is generally defined as a systolic blood pressure (the “top number”) greater than or equal to 140 mm Hg, or/and a diastolic blood pressure (the “bottom number”) greater than or equal to 90 mm Hg. As we age, our blood pressure tends to gradually rise, and by the time we reach our 60s, the majority of us will have elevated blood pressure. Hypertension is known as “the silent killer” for good reason, as it can cause gradual, asymptomatic, and irreversible damage to the body’s vital organs, including the heart, brain, and kidneys, if left untreated.
More than 240 African-American and Caucasian women participating in a large prospective study (the National Heart, Lung and Blood Institute Growth and Health Study) were evaluated in this smaller study. All of these women were between 18 and 21 years of age when they enrolled in this large public health study. During their 10th year of participation in this ongoing clinical study, blood levels of Vitamin C were measured in all of these women. Blood pressure readings during the 9th and 10th years of participation were then analyzed as a function of Vitamin C levels in the blood of these 242 patient volunteers. These patient volunteers were then divided into 4 groups, based upon the level of Vitamin C in their blood.
The women in the group with the highest blood levels of Vitamin C had, on average, significantly lower systolic and diastolic blood pressure readings when compared to the women in the group with the lowest Vitamin C levels, even after adjusting for differences between the two groups of women in terms of other hypertension risk factors like race, obesity, dietary intake of fat and salt, and education levels. The average systolic blood pressure among the women with the highest levels of Vitamin C in their blood was almost 5 mm Hg lower than the systolic blood pressure among the women with low Vitamin C levels. Likewise, the average diastolic blood pressure reading among the women with highest Vitamin C levels was 6 mm Hg lower than what was observed among the women with very low Vitamin C levels in their blood.
When blood pressure readings in the 10th year of this study were compared with the blood pressure results from the previous year, higher Vitamin C levels also appeared to be associated with a smaller annual increase in blood pressure when compared with very low Vitamin C levels.
Thus, in this prospective clinical research study, high levels of Vitamin C in the blood appeared to be linked with, on average, lower blood pressure readings and with significantly less increase in blood pressure readings over a period of one year.
While the results of this cohort study are very intriguing there are, as always, a few caveats that must be mentioned. First of all, this study did not link dietary Vitamin C intake with Vitamin C levels in the blood, so it is not possible to know, from this study, if a diet rich in vitamin C (which is rapidly excreted from the body following ingestion) resulted in the higher blood levels of this vitamin that were observed, or if there are other factors, including genetic factors, that determine a person’s average Vitamin C levels in the blood. Similarly, if genetic factors are primarily responsible for the level of Vitamin C in the blood, these same genetic factors could also be affecting blood pressure independent of any direct action by Vitamin C. Also, while this study of young women strongly suggests that high levels of Vitamin C in the blood may decrease the natural rise in blood pressure that occurs with aging, it cannot yet tell us if these favorable changes in blood pressure, presumably due to Vitamin C, will be sustained as these women grow older. This study also cannot tell us whether or not, in the long run, the apparently favorable effects of Vitamin C on blood pressure will actually lead to any clinically significant improvements in health, either.
Given the recent
drumbeat of dismal news regarding the
antioxidant vitamins and other related dietary supplements, this small
does offer some hope that Vitamin C might still be associated with
health benefits beyond its primary role in the synthesis of collagen (a
critical structural protein found throughout the body).
However, it will take many more years before
we know whether or not Vitamin C supplementation can truly reduce the
inexorable rise in blood pressure that occurs with aging, and if so,
not this effect has any clinically meaningful impact on health.
Copyright 2009. Robert A. Wascher, MD, FACS.
All rights reserved.
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